1. Field of the Invention
The present invention is directed to novel radiation sensitive compositions and their use in photographic elements. More specifically, this invention is directed to such elements and compositions including nucleating agents and silver halide grains capable of forming internal latent images.
2. Description Relative to the Prior Art
Photographic elements which produce images having an optical density directly related to the radiation received on exposure are said to be negative working. A positive photographic image can be formed by producing a negative photographic image and then forming a second photographic image which is a negative of the first negative--that is, a positive image. The advantage of forming a positive photographic image directly has long been appreciated in the art. A direct-positive image is understood in photography to be a positive image that is formed without first forming a negative image.
A conventional approach to forming direct-positive images is to use photographic elements employing internal latent image forming silver halide grains. After imagewise exposure, the silver halide grains are developed with a surface developer--that is, one that will leave the latent image sites within the silver halide grains substantially unrevealed. Simultaneously, either by uniform light exposure or by the use of a nucleating agent, the silver halide grains are subjected to development conditions that would cause fogging of a negative-working Photographic element. The internal latent image forming silver halide grains which received actinic radiation during imagewise exposure develop under these conditions at a comparatively slow rate as compared to the internal latent image forming silver halide grains not exposed. The result is a direct-positive silver image. In color photography the oxidized developer that is produced during development is used to produce a corresponding positive dye image. Multicolor direct positive photographic images based on the above-described "internal image reversal" process have been investigated extensively in connection with image-transfer photography.
The term "nucleating agent" is employed herein in its art recognized usage to mean a fogging agent capable of permitting the selective development of internal image forming silver halide grains which have not been imagewise exposed, in preference to the development of silver halide grains having an internal latent image formed by imagewise exposure. Nucleating agents are fogging agents which perform essentially the same function achieved by uniform light exposure during development in internal image reversal processes.
Substituted hydrazines have been extensively investigated as nucleating agents for forming direct-positive photographic images with internal latent image emulsions. Illustrative patents directed to the use of hydrazines in forming direct-positive photographic images are Ives U.S. Pat. Nos. 2,563,785 and 2,588,982, issued Aug. 7, 1951 and Mar. 11, 1952, respectively; Whitmore U.S. Pat. No. 3,227,552, issued Jan. 4, 1966; and Knott and Williams British Patent No. 1,269,640, published Apr. 6, 1972. Ives as well as Knott and Williams teach the incorporation of their nucleating agents in photographic developers. The nucleating agents of Whitmore can be incorporated directly within a photographic element or in an image-receiving element as well as in the photographic developer. Whitmore teaches the use of substituted hydrazine nucleating agents in image transfer type photographic elements.
Another class of useful nucleating agents are the acylhydrazinophenylthioureas disclosed by Leone, Weber and Wrathall U.S. Pat. No. 4,030,925, issued June 21, 1977.
In considering the formation of direct-positive photographic images using conventional substituted hydrazine nucleating agents of the type disclosed above, a number of disadvantages have been identified. One disadvantage has stemmed from the tendency of incorporated hydrazine derivatives when used in conventional large quantities to liberate nitrogen gas in the course of nucleating silver halide. The liberated gas can result in bubbles being trapped within the binder for the photographic element. The bubbles can produce optical distortions or even cause discontinuities in one or more layers of the photographic element, thereby degrading the photographic image.
Another approach toward finding useful nucleating agents has been to synthesize heterocyclic nitrogen quaternary salts, such as disclosed by Kurtz and Harbison U.S. Pat. No. 3,734,738, issued May 22, 1973, and Kurtz and Heseltine U.S. Pat. No. 3,719,494, issued Mar. 6, 1973. Similarly, Lincoln and Heseltine U.S. Pat. Nos. 3,615,615 and 3,759,901, issued Apr. 13, 1970 and Sept. 18, 1973, teach the use of novel N-hydrazonoalkyl substituted heterocyclic nitrogen quaternary salts as nucleating agents. While these heterocyclic nucleating agents have reduced the concentrations required somewhat, they have generally shared the above-described disadvantages of substituted hydrazine nucleating agents. Further, these quaternary salts can be disadvantageous in absorbing light within the visible spectrum.
U.S. Pat. No. 3,347,671 issued Oct. 17, 1967 to W. M. Salminen discloses reductone derivatives useful as fogging agents for use in conjunction with silver halide emulsions that form latent images predominantly inside the silver halide grains when such emulsions are utilized in color diffusion transfer processes.